The present invention relates to an apparatus for simulating a color printing process comprising a scanning unit such as a flying spot scanner with a cathode ray tube or a television camera for scanning a set of color separation films of cyan, magenta, yellow and black to derive subtractive primary color signals of cyan, magenta, yellow and black, a control and process unit for receiving the thus derived subtractive primary color signals and adjusting and processing them to derive three additive primary color signals of red, green and blue, and a color monitor unit for receiving the thus derived additive primary color signals and displaying on its screen a color image which simulates a color print image.
By means of such a simulating apparatus, while inspecting the color image displayed on the monitor screen, accurate perception and estimation of color reproduction quality, preproof study of color images, inspection of color balance, etc. can be effected and simulation of the color printing process can be carried out.
There have been developed several apparatuses for simulating the color printing process. In Japanese Patent Application Publication Nos. 4,777/76 and 40,961/79, and U.S. Pat. No. 3,128,333, such apparatuses have been disclosed. For instance, in an apparatus described in Japanese Patent Application Publication No. 4,777/76, onto four color separation films of cyan, magenta, yellow and black are projected raster images of a flying spot scanner by means of four optical systems and light rays transmitted through the respective films are separately received by photomultipliers to derive four subtractive primary color image signals of cyan, magenta, yellow and black. Then after these image signals have been suitably processed and adjusted, they are converted into three additive primary color image signals of red, green and blue which can be displayed on a color monitor for simulating the printing process or printing colors. In such an apparatus it should be taken into account that color reproduction principles are entirely different for color prints and color images on the monitor. Therefore the subtractive primary color signals obtained by scanning the set of color separation films have to be converted into the additive primary color signals usable in the color monitor. Various methods for effecting this conversion have been developed and proposed. For instance, one effective method is described in a book entitled PRINCIPLES OF COLOR REPRODUCTION written by J. H. Yule, published by JOHN WILEY & SONS, INC. In this known method there has been taken into account how to process the subtractive primary color signals in order to reproduce, on the color monitor comprising a usual color cathode ray tube, the color image which resembles the real printing colors as closely as possible. That is to say, the known methods have stressed in the case of using the normal color cathode ray tubes which have been installed in the usual color television receiver and color monitors, how to convert the subtractive primary color signals derived by scanning the set of color separation films into the color television signal. This may be also applied to the color printing process simulating apparatuses described in the above mentioned Japanese Patent Application Publication No. 40,961/79 and U.S. Pat. No. 3,128,333. These known apparatuses comprise the color monitors including the normal color cathode ray tubes. The inventors of the instant application have found after various examinations and considerations that when use is made of the normal color cathode ray tube and the subtractive primary color signals are converted into the color television signal, it is impossible to simulate the printing colors with a high fidelity. The inventors have further investigated the undesirable phenomena and found the following two major causes. In the color printing process simulating apparatus it is necessary to provide a relatively large cathode ray tube having a screen of about twenty inches, and in order to inspect precisely details of the images it is required to look at the screen from a position spaced from the screen by about 50 to 70 cms. Therefore, scanning lines are liable to be visible. In the usual television receivers, it is advisable for viewers to situate themselves in front of the receivers at a distance equal to four or five times the diameter (diagonal) of the screen. Contrary to this, in the simulating apparatus it is required for the viewer to see the screen that he be much nearer to the screen. Therefore, when the usual color cathode ray tube of 525 lines per frame for the NTSC standard system, i.e. 1.6 lines per millimeter, the scanning lines appear as distinctive lines. In such a case black lines are clearly visible between successive luminous lines and thus an operator might experience difficulty in inspecting and estimating the displayed color image. Moreover, the operator might misjudge the real colors and experience difficulty in comparison between the printing colors and the displayed color image. In this manner an accurate correction, adjustment and calibration could not be expected by means of the usual color cathode ray tube. As a result, the advantage of using the large cathode ray tube might be lost. Moreover, when the scanning lines are visible, the operator might become tired to a great extent.
Secondly, the inventors have found that the usual color cathode ray tube could never reproduce inherently the printing colors in an accurate manner. In order to simulate the printing colors completely, the color reproduction range of the color cathode ray tube should include all or substantially all of the color reproduction range of the printing colors. However, upon comparing the color reproduction regions of the color printing and the usual color cathode ray tube, it has been confirmed that green and cyan colors of the color printing could never be reproduced by the usual color cathode ray tube.
As explained above, since the known color printing process simulating apparatus includes a color cathode ray tube which has limited resolution and color reproducibility, how to improve the process for converting the subtractive primary color signals obtained by scanning the set of color separation films into the color television signal, it is impossible to reproduce the color image which simulates the printing colors with a high fidelity.